docs: remove v2 notice from top of README

The v2 rework banner at the top of README.md is no longer needed now that v2 is released.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KRZ4537QQR9yexj3gZGcYu

Author: claude

README.md

@@ -13,13 +13,6 @@
 
 </div>
 
-> [!NOTE]
-> **This is v2 of the MCP Python SDK, the current stable release line.** It is a major rework of the SDK, both to support the [2026-07-28 MCP specification](https://modelcontextprotocol.io/specification/2026-07-28) (and every earlier revision) and to fix long-standing architectural issues. Coming from v1? See [What's new in v2](https://py.sdk.modelcontextprotocol.io/whats-new/) for the tour of what changed and the [migration guide](https://py.sdk.modelcontextprotocol.io/migration/) for every breaking change.
->
-> **Not ready to migrate?** v1.x lives on the [`v1.x` branch](https://github.com/modelcontextprotocol/python-sdk/tree/v1.x), continues to receive critical bug fixes and security patches, and is documented at <https://py.sdk.modelcontextprotocol.io/v1/>. Since `pip install mcp` now installs 2.x, keep a `<2` upper bound on your requirement (for example `mcp>=1.28,<2`) until you've migrated.
->
-> Something rough, confusing, or broken? [Open an issue](https://github.com/modelcontextprotocol/python-sdk/issues/new?template=v2-feedback.yaml) or find us in [#python-sdk-dev on the MCP Contributors Discord](https://discord.gg/6CSzBmMkjX).
-
 ## Documentation
 
 **The documentation lives at <https://py.sdk.modelcontextprotocol.io/>.**